1. Field of the Invention
This invention relates generally to the field of facsimile data transmission. More particularly, the present invention relates to a system and method for adjusting and optimizing the transmission rate for facsimile in a FAX Relay system based on available network bandwidth. The present invention also relates to a method and apparatus for maintaining a fax transmission over a communications path that includes a narrowband network, by using a mechanism to determine the available bandwidth and dynamically adjusting facsimile flow control based on the available bandwidth. In particular, the present invention relates to a method and apparatus for maintaining a fax transmission even though a data bottleneck exists somewhere between a source and destination fax machine, which might otherwise cause the fax transmission to cease or fail due to excessive time delay caused by the bottleneck.
2. Description of the Related Art
The Telecommunication Standardization Sector(ITU-T) of the International Telecommunications Union (ITU) has defined Procedures for document facsimile transmission in the general switched telephone network in T.30 and T.4 standards. T.30 and T.4 define Group 3 facsimile service, also known as Group 3 FAX and G3 FAX. The recommendation is for xe2x80x9cGroup 3 facsimile apparatus.xe2x80x9d Group 3 facsimile apparatus includes facsimile machines, computers with fax modems and appropriate software, as well as other products. As referred to herein, the term xe2x80x9cFAX machinexe2x80x9d applies to any Group 3 facsimile apparatus. To facilitate understanding of the context of the present invention, the T-4 and T-30 standards are incorporated herein in their entirety.
T.30 was written for facsimile service provided over a wired telephone network, a Public Switched Telephone Network (PSTN), or a digital encoding of the analog signal such as the PCM. However, in a network in which channels are assigned low rate digital streams such as a TDMA system or a packet based system with limited bandwidth, other techniques are used to send a FAX in real-time. In order to support Group 3 FAX over such Bandwidth Limited Digital Networks (BLDNs), a FAX relay system (sending side) can be employed to demodulate the FAX analog signal and transmit digital data using the digital network and re-modulate the signal at the other relay station (receiving side) to analog signal. In such systems, in addition to demodulating and re-modulating the facsimile signal, the T.30 based relay protocol is implemented in the fax relay gateways.
When such systems can allocate bandwidth from a call to another call, It is desirable to have methods and systems to detect the network congestion information, such as, available bandwidth, network delay, and network jitter information and automatically adjust the rate of a FAX transmission in real-time to the real time changes in the corresponding network congestion information, such as, the available bandwidth, network delay, and network jitter.
FIG. 1 shows a system by which two facsimile terminals communicate with each other, whereby a digital (or other narrowband) network is utilized in the communications path between the two fax terminals. A first fax terminal (or machine) 11-1 is communicatively connected to a first private branch exchange (PBX) 13-1, whereby the PBX 13-1 is communicatively connected to a first gateway processor (or fax relay) 14-1. In other embodiments, the PBX 13-1 may alternatively be a PSTN or a plain old telephone system (POTS). The PBX 13-1 may also be connected to a data modem 12-1 and/or a telephone 10-1. The first gateway processor 14-1 provides connectivity with a narrowband network 15, which is shown, for example, as a digital network in FIG. 1. In one embodiment, the digital network may be a packet network.
Fax data is typically transmitted over conventional analog telephone lines, such as those used by a PSTN or PBX, using 64 bit-per-second pulse code modulation (PCM). The PCM-modulated fax data (analog data) needs to be converted to a different form, that is, into digital data, by the first gateway 14-1, so that the digital data can be output, for example, in packets over the digital network 15.
A second gateway (or fax relay) 14-2 provides a communicative connection to a second PBX 13-2, which provides a communicative connection to a second fax terminal (or machine) 11-2. Like the first PBX 13-1, the second PBX 13-2 may alternatively be a PSTN or a POTS. The second PBX 13-2 may also be connected to a data modem 12-2 and/or a telephone 10-2. The second gateway 14-2 receives digital data from the digital network 15, for example, in packet form, and converts the digital data into analog data having a PCM format. The PCM data is then sent over the second PBX 13-2, through which it is received by the second fax 11-2.
The digital network 15 is typically of a narrower bandwidth than the analog portions (PBX 13-1, 13-2) of the communications path between the first and second faxes 11-1, 11-2. As such, there exists a problem exists in that the digital network 15 may become a bottleneck with respect to fax data being sent between the first and second faxes 11-1, 11-2.
If the channel rate or packet throughput of the digital network 15 is equal to or greater than the native fax rate (e.g., 2400, 4800, 9600, or 14,400 bps) between the first and second faxes 11-1, 11-2, a demodulation-remodulation relay may be used. However, a problem may arise when the channel rate or packet throughput is less than the native rate of the fax machines. As discussed above, this may lead to delays in the fax transmission, which may in turn cause the fax transmission to cease due to excessive time between receipt of fax data at the fax machines since most fax protocols have built-in timing requirements that cause the fax transmission to be terminated (or retried) if the time delay exceeds certain predefined threshold values.
Therefore, it is a general object of the invention to alleviate the problems and shortcomings identified above.
In a general aspect, the present invention provides a method of fax transmission over a fax relay network that includes at least an analog portion and a digital portion of the fax relay network, the method including: receiving, at a first fax relay gateway that communicatively connects a sending fax machine to the digital portion of the fax relay network, image data from the sending fax machine; converting the image data into digital data to be sent over the digital portion of the fax relay network; storing the digitized image data in a buffer at the first fax relay gateway; outputting the digitized image data in accordance with a data rate of the digital portion of the fax relay network, the digitized image data being received by a second fax relay gateway on the digital portion of the fax relay network, the second fax relay gateway communicatively connecting a receiving fax machine to the digital portion of the fax relay network; determining an amount of data stored in a buffer at either the first fax relay gateway or the second fax relay gateway, or determining the amount of jitter in the received data packets and determining if the amount of the jitter in the reception of packets from the digital network is greater than a predefined threshold; and monitoring the reception of a message confirmation (MCF) message from the receiving fax machine after the reception of a page; wherein if the determination made of the amount of data stored in the buffer at either the first fax relay gateway or the second fax relay gateway, is that the amount of data stored in the buffer is greater or less than a particular threshold, or that the determination is that the amount of jitter in the reception of packets from the digital network is greater than the predefined threshold, forcing the sending fax machine to initiate a procedure to adjust the transmission data.
In another aspect, the present invention provides forcing the sending fax machine to initiate a procedure do adjust the transmission data rate by replacing the MCF from the receiving fax machine with an RTP (retrain positive) message prior to transmission of a next fax page.
In another aspect, the present invention provides that the sending fax machine is communicatively connected to a first public switched telephone network, the first public switched telephone network communicatively connecting the sending fax machine with the first fax relay gateway.
In a further aspect of the present invention, the receiving fax machine is communicatively connected to a second public switched telephone network, the second public switched telephone network communicatively connecting the receiving fax machine with the second fax relay gateway.
In one aspect of the present invention, the image data received by the first fax relay gateway is converted from pulse-code-modulated format to digital format, by the first fax relay gateway, and the digital data received by the second fax relay gateway is converted from digital format to pulse-code-modulated format, by the second fax relay gateway.
In another general aspect, the present invention provides a method of fax transmission over a fax relay network that includes at least a wideband portion and a narrowband portion, the method includes: receiving, at a first fax relay gateway that communicatively connects a sending fax machine to the narrowband portion of the fax relay network, image data from the sending fax machine; storing the image data in a buffer at the first fax relay gateway; outputting the digitized image data in accordance with a data rate of the narrowband portion of the fax relay network, the digitized image data being received by a second fax relay gateway on the digital portion of the fax relay network, the second fax relay gateway communicatively connecting a receiving fax machine to the digital portion of the fax relay network; determining an amount of data stored in the buffer at the first fax relay gateway, or determining the amount of jitter in the received data packets and determining if the amount of the jitter in the reception of packets from the narrowband network is greater than a predefined threshold; and monitoring the reception of a message confirmation (MCF) message from the receiving fax machine after the reception of a page; wherein if the determination made of the amount of data stored in the buffer at the first fax relay gateway or in a buffer at the second fax relay gateway, is that the amount of data stored in one of the two buffers is greater or less than a particular threshold, or that the determination is made that the amount of jitter in the reception of packets from the narrowband network is greater than a predefined threshold, replacing the MCF from the receiving fax machine with an RTP (retrain positive) message to force the sending fax machine to initiate a retrain procedure prior to the transmission of the next fax page.
In one aspect of the present invention, the narrowband portion is a digital network while the wideband portion is an analog network.
In another aspect of the present invention, the fax relay gateway is a multi-channel system with a single processor handles voice/fax/data calls wherein a collocated process determines the available bandwidth and notifies a channel processor.
In a further aspect of the present invention, the detection of a fax signal in voice by the channel processor is used to determine the need to request for bandwidth adjustment from the collocated process, wherein the detection of the FAX in a voice channel may include decoding of the ITU-T specified V.8 CM and JM sequence,
In one aspect, the present invention provides that a local process at the gateway determines the available bandwidth and notifies a channel processor.
In another aspect, the present invention provides that a probing mechanism determines network delay, bandwidth and packet jitter on a call-by-call basis at the start of a facsimile call, wherein the probing mechanism may include transmission of data from the first relay gateway to the second relay gateway or transmission of data from the second relay gateway to the first relay gateway.
In one aspect of the present invention, the probing mechanism probes network delay, bandwidth and packet jitter prior to the pre-message procedure defined in the International Telecommunications Union Telecommunications Standardization Section (ITU-T) Recommendation T.30.
In a further aspect of the present invention, the amount of network delay, bandwidth, or jitter in the reception of probing signals from the digital packet network is used to manipulate the Digital Identification Signal (DIS) signal from the receiving fax machine to the sending fax machine, wherein the DIS signal is manipulated by choosing a lower fax transmission rate.
In another aspect of the present invention, the amount of network delay, bandwidth or jitter in the reception of probing signals from the digital packet network is used to manipulate a Training Check Function (TCF) signal at one of the fax relay gateways.
In a further aspect of the present invention, the TCF training sequence following a pre-message handshake is corrupted by either the first fax relay gateway or the second fax relay gateway to force the end-to-end fax transmission rate to accommodate the digital network bandwidth, delay and jitter characteristic.
In another aspect of the present invention, if a first corruption of the TCF training sequence does not reduce the fax transmission rate to a pre-determined rate, a subsequent TCF sequence is corrupted by either the first or the second fax relay gateway.
In one aspect of the present invention, a real-time monitoring of the network throughput, delay and packet jitter during the transmission of a page by the first or second fax gateway is used to force a rate renegotiation for subsequent fax transmission pages by replacing the MCF with an Retrain Positive (RTP) message.
In another important aspect, the present invention provides a system for fax transmission over a fax relay network that includes at least a wideband portion and a narrowband portion, the system including :a first fax relay gateway communicatively connecting a sending fax machine on the wideband portion of the network to the narrowband portion of the network, the first fax relay gateway receiving image data from the sending fax machine and outputting digitized image data in accordance with a data rate of the narrowband portion of the fax relay network; and a second fax relay gateway, communicatively connecting a receiving fax machine to the narrowband portion of the network, wherein at least one of the first fax relay gateway or the second fax relay gateway includes a control process that determines whether an amount of data stored in a buffer in the fax relay gateway is greater or less than a particular threshold or determines that the amount of jitter in the narrow band network exceeds a particular threshold, and if so, initiates a retrain procedure to adjust the fax data rate.
In one aspect of the present invention, one of the first fax relay gateway or the second fax relay gateway includes a single Digital DSP running the control process and at least one channel processor.
In another aspect of the present invention the channel processor includes a voice/fax/data detector that detects a fax signal in a voice channel and the detection of the fax signal is used by the control process to determine bandwidth to be allocated to that channel processor.
In a further aspect of the present invention, the channel processor comprises a fax modem and a T-30 based fax relay protocol processor to control fax transmissions from the channel processor, wherein the channel processor further comprises a bandwidth adapter that adjusts the fax transmission rate from the channel processor.
In another aspect of the present invention, the control process runs on a processor separate from a Digital Signal Processor (DSP) that runs a channel processor.